1. Field of the Invention
The present invention relates to lighting poles. More specifically, the invention relates to a vibration isolating bracket arm assembly mounted to the lighting pole for supporting a light fixture.
2. Related Art
It is known to provide a street lamp with a vertical post, a transverse arm pivotally attached to the vertical post and supporting a lighting device, and even, as shown in U.S. Pat. No. 5,171,088 to provide a second arm attached to the vertical post and the transverse arm for the purpose of adjusting the angle of the transverse arm relative to the vertical post. However, known lighting pole structures have experienced the problem of premature lamp failure as a result of excessive vibrations of the lighting poles. Vibration of structures on which the lighting poles are mounted, such as bridges, sometimes produces first, second and third mode vibrations of the lighting poles. The natural frequencies of these lighting poles typically range between one cycle per second (during a first mode vibration) and fifteen cycles per second (during a third mode vibration). Vibration of the lighting pole is most severe when the natural frequencies of the structure supporting the lighting pole are at or near one or more of the natural frequencies of the lighting pole. When a lighting pole is mounted on a bridge or highway overpass, vibration is caused by passing vehicles. This vibration is primarily vertical in direction and often results in premature lamp failure or failure of bracket arms supporting the lamps.